Crossflow microfiltration systems play a major role in the treatment of water and wastewater for domestic and industrial purposes. Ceramic crossflow microfiltration has been applied to several industrial produced water systems in recent years. The success of the ceramic crossflow microfiltration system in producing industrial waters is dependent on the process performance, along with the operational and maintenance parameters.
Advanced water filtration systems are rapidly becoming more widely used for treating industrial and domestic water. Several of the more advanced systems incorporate crossflow microfiltration systems (CFM). CFM is a new branch of membrane technology which filters particles from liquids of a size between conventional filtration and ultrafiltration. In the CFM process, feed water is passed tangentially across the surface of a porous membrane, as shown in FIG. 1. The feed water enters the tube and product water passes tangentially through the circular membrane channels. The solids which are filtered out form a dynamic membrane along the wall of the tube (membrane) which is constantly eroded and moved by the hydrodynamic shear exerted by the cross flow, which causes reentrainment of particles from the dynamic membrane into the feed/recycle flow. This continuous cross flow action, and accompanying hydrodynamic shear, reduces the concentration of the suspended solids at the membrane surface, and permits passage of the suspended solids across the face of the membrane with minimal fouling and clogging at the membrane solids interface.
It has been found that in many cases there is a rapid decrease in the filtration rate, in spite of high crossflow velocities. The reason for this phenomenon is the wide range of particle sizes in the suspension, the finest particles often being smaller than the membrane pore size which results in membrane penetration and subsequent pore structure clogging. In order to minimize the effect of this phenomenon, another step is conventionally added to the process, i.e. the pulsed backflushing of the membrane. This backflushing is a periodic rapid reversal of flow direction through the membrane. This arrangement is illustrated in FIGS. 2 and 3 herein. This momentary flow reversal generally cleans up the surface of the membrane and allows the particles to be swept away in the cross flow of the liquid.
Current CFM systems use a backpulse system which is complex and has several inherent operational problems. Conventional backpulse systems pump product water, from a small storage tank, into an accumulator backpulse tank so that the accumulator tank has a pressure of twenty to fifty p.s.i. higher than the CFM operating system pressure. To provide a rapid flow reversal, the accumulator tank must contain an inert compressible gas, normally nitrogen. As a result, numerous valves, pressure switches, level gages, and a programmable logic controller are required to operate the system.
It is an object of the present invention to provide a filtration system that ensures that fresh filter fluid is used for the backpulsing.
It is another object of the present invention to provide a filtration system that eliminates cool down and/or post-precipitation of the permeate fluid.
It is a further object of the present invention to provide a filtration system that optimizes the volume of permeate fluid used for backflushing.
It is another object of the present invention to minimize the number of components required for the proper backpulsing of the filter.
It is still another object of the present invention to provide a backpulse system that is easy to control, easy to use, and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.